Many internal combustion engines utilize fuel injectors to introduce combustible fluids into the intake manifolds or combustion chambers of the engine. Electronic controls are often utilized to govern operation of the fuel injectors. To allow appropriate interaction between the injector valve structure and the electronic controls, such injectors typically include a solenoid operated valve that can respond to electric signals from the electronic controls.
The electronic controls for such prior art fuel injector systems generally include a current sense unit that can provide a signal indicative of the level of current flowing through the injector solenoid. An injector drive control unit receives these signals and injection command signals and determines when to apply power to the injector solenoid. The injector drive control unit can then apply a drive signal when appropriate to an injector drive unit. The injector drive unit operates to selectively allow current to flow from a power source (such as a battery) through the injector solenoid and the injector drive unit.
Such prior art systems also usually include a flyback control unit. Although current flow through an inductor cannot be halted in an instant, the flyback control unit provides a means for the stored energy in the solenoid coil to be quickly dissipated and thereby assure a speedy response of the injector valve itself.
These prior art injector drive control units typically operate by comparing the current sense signal with a threshold signal. The threshold signal can usually be varied to provide for both a peak initial current and a lower subsequent holding current. Many of these devices also operate to switch the injector drive unit on and off in planned succession to maintain the solenoid current within either a peak current range or holding current range.
Depending upon the dynamics and operating means of the fuel injection system in question, some of these prior art solutions may not be appropriate. For example, there exists a need for an injector driver control unit that can maintain a minimum solenoid current during both the peak and holding current phases, while also using time as an operative control parameter to ensure the creation and maintenance of the desired control waveform.